it is known to use TiB2 as a coating material for tools. For example, U.S. Pat. No. 4,820,392 describes how a sputtering process is used to deposit a layer of TiB2 onto tools. Although the material deposited in this way does feature good mechanical and tribological properties, the industry is seeking ways to achieve a higher density and even greater hardness.
Since TiB2 is a material with a very high melting point, using so-called cathodic arc vaporization, which would result in denser and therefore harder layers, is not economically feasible.
One known option for shifting the density and hardness of sputtered layers into ranges similar to those produced by arc vaporization is the so-called HiPIMS process. (HiPIMS=High Power Impulse Magnetron Sputtering). With this sputtering process, a sputtering cathode is acted on with high power pulse densities, which results in the fact that the material that is vaporized from the cathode has a high percentage of ionization. If a negative voltage is then applied to the work piece that is to be coated, these ions are accelerated toward the work piece, thus producing very dense coatings.
The sputtering cathode must be acted on with power in a pulsed fashion in order to give it time to dissipate the heat input that accompanies the power. In the HiPIMS process, a pulse generator is therefore used as the power source. This pulse generator must be able to output pulses that are very powerful, but very short. The pulse generators available today do not have much flexibility when it comes to pulse height and/or pulse duration, for example. Ideally, rectangular pulse should be output. Usually, though, the power output within a pulse is very time-dependent, which has a direct influence on the layer properties such as hardness, adhesion, internal stress, etc. In addition, the coating rate is negatively influenced by the deviation from the rectangular profile.
In particular, these difficulties raise questions with regard to reproducibility.